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Does Water Expire?

Water is one of the most abundant substances on the planet, covering nearly 71% of the earth’s surface. It is also one of, if not the, most vital substances—both for our health and for the health of the environment.

Off-grid RVs, boats, and cottages are faced with the challenge of regular access to safe, potable water. Many North Americans choose to filter water in bulk, housing it in water storage tanks for future use.

In theory, this sounds like a future-proof solution, but it begs an important question: does water expire?

Water Storage: The Facts

The short answer to this question is no, water itself does not expire. The expiration date you’ll find on bottled water is more of a regulatory requirement than anything (although plastic has been found to leach impurities over time). However, microbial organisms (bacteria, viruses, germs, and the like) will build up when water sits stagnant and unused. Those of you who leave a glass of tap water on your bedside table overnight may have noticed its taste will change over the course of as little as 12 hours. This is caused by carbon dioxide and airborne bacteria mixing with the water and tampering with its pH.

Of course, storage tanks are sealed containers, but does this variable eliminate the problem? A peer-reviewed study by the American Water Works Association compared four water tanks of different materials. Their goal was to better understand exactly how water’s chemistry changes when it is stored over a span of time.

Here’s what the researchers found:

Water quality can change in as few as 96 hours – Within 4 to 7 days, the chemical characteristics of tank water shifted dramatically. These changes were attributed largely to a loss of chlorine and an increase in pH, both of which lead to an increase of HPCs (heterotrophic plat counts, used to measure the overall bacteriological quality of drinking water).

Non-continuous water flow negatively impacts water quality – With high HPC measurements comes an increase in bacterial species, something that may be attributed to bacteria’s ability to slowly grow under low-nutrient water conditions.

The tanks themselves come with a separate set of needs: to optimize effectiveness, water storage tanks must be fabricated using high-integrity materials, and undergo regular inspection and cleaning. It’s no surprise, then, that AWWA recommends the public limit traditional water storage methods, and instead consider alternative options.

Because water is cleanest at the point of use, purification methods that work immediately prior to consumption are the safest, most reliable way to guarantee potable water. Technologies like ultraviolet (UV) and light emitting diodes (LED) have both proven their ability to eliminate potentially harmful microorganisms, and joining these two techniques provides safe and reliable drinking water. Learn more about this water purification technology here.